darragh, in astronomical terms, I think dedicated scopes would give more performance for much less cost. The lens would have AF, but that isn't really needed for sky work. Roughly speaking, assuming the optics are of sufficient quality, the resolution is limited by diffraction, which eventually comes down to how big it is on the front. 1200mm f/5.6 is only just over 8 inches. A 12 inch dobsonian can be had for less than a 7D body, and a 12 inch Ritchey-Chrétien with mount is less than a 1Ds3.

Some samples... the first 5 are camera jpeg resized only with no further processing.

A thin moon... taken with camera at scope prime focus.

From same set as above, but this time using a 2x barlow for effectively 2650mm f/26. Even scaled down here you can see diffraction softening. It is still worth it

This is what the contrast looks like when the sky was still relatively light.

As above + 2x barlow again.

To give an idea of the size of the moon relative to focal length. Note the moon varies in distance, and therefore size from the earth. When it is close, it is too big to fit in a single shot on 1.6x crop sensor. Here it only just fits.

Also check out the best moon thread where I have posted two other examples. One shows the best resolution I ever got from the scope, the other is when I went for colour cleanness. Both of those involved processing.

This is no different than with photographic lenses. While bigger pixels (regardless of sensor size) will be diffraction limited later, a bigger sensor gives you get a bigger field of view so need more focal length to get the equivalent detail. For a constant physical aperture typical of most scopes, you trade focal length and photographic aperture so it works out about the same. Fundamentally, need bigger scope.

That reminds me, I wanted to try the 5D to see what the image circle of the scope output is like...

Edit: here's a test shot on the 5D, taken with the rear adapter (not eyepiece adapter).

It's not practical for terrestrial stuff. 1325mm f/13 is incredibly long and slow. You'll need a fast shutter aided by high ISO, and a stable platform. Plus, it is manual focus. Also, while it can focus close, at typical working distances even the air quality will impact the final result. You can see heat haze ripples for example, and reducing contrast as you focus further.

So it is not impossible, but unless you're photographing distant stationary subjects in good conditions, it isn't really practical.

This scope is primarily sold for night sky observation where these factors are not so significant a limitation.